As mobile devices have been increasingly developed, and the demand of such mobile devices has increased, the demand of secondary batteries has also sharply increased. Among them is a lithium secondary battery having high energy density and operating voltage and excellent preservation and service-life characteristics, which has been widely used as an energy source for various electronic products as well as the mobile devices.
On the other hand, various kinds of combustible materials are contained in the lithium secondary battery. As a result, the lithium secondary battery may be heated or explode due to the overcharge of the battery, the overcurrent in the battery, or other physical external impacts. That is, the safety of the lithium secondary battery is very low. Consequently, a protection circuit module (PCM) for effectively controlling an abnormal state of the battery, such as the overcharge of the battery, is loaded on a battery cell while being connected to the battery cell.
Generally, the PCM is connected to the battery cell via conductive nickel plates by welding or soldering. That is, the nickel plates are connected to electrode tabs of the PCM by welding or soldering, and then the nickel plates are connected to corresponding electrode terminals of the battery cell by welding or soldering. In this way, the PCM is connected to the battery cell to manufacture a battery pack.
It is required for safety elements, including the PCM, to be maintained in electrical connection with the electrode terminals of the battery cell and, at the same time, to be electrically isolated from other parts of the battery cell. Consequently, a plurality of insulative mounting members or a plurality of parts are required to construct such connection, with the result that the battery pack assembly process is complicated, and a space for receiving the battery cell decreases.
Also, a large number of welding or soldering processes are required to construct the battery pack, and the welding or soldering processes must be carried out with high precision because of the small structure of the secondary battery. As a result, a defect possibility is great. Furthermore, the welding or soldering processes are added during the manufacturing process of a product, which increases the manufacturing costs.
Consequently, research has been actively made on a technology for reducing the number of parts loaded on the top of the battery cell and increasing the capacity of the battery cell. For example, Korean Patent Application Publication No. 2004-0021308 discloses a closed type secondary battery including an electrode assembly having anode plates, cathode plates, and separators for insulating the anode plates and the cathode plates from each other, respectively, a container for receiving the electrode assembly, the container having an opening formed at one surface thereof, a first round surface provided at one side thereof, and a first flat surface provided at the other side thereof opposite to the first round surface, and a cap assembly for electrically connecting at least one electrode plate, among the anode plates and the cathode plates, to the outside, the cap assembly having a cap plate for sealing the opening of the container, wherein a safety element is attached to the first flat surface.
The above-described technology has an advantage in that the safety element is attached to the outer surface of the battery container, i.e., the first flat surface of the battery container, whereby it is possible to easily attach the safety element to the secondary battery. However, the disclosed technology has a problem in that the total volume of a battery pack, in which the secondary battery is mounted, increases.
Consequently, there is a high necessity for a technology that is capable of reducing the number of members mounted to the top of the battery cell to simplify the assembly process, reducing the number of welding processes to decrease a defect rate, achieving stable coupling between the members loaded on the top of the battery cell, and increasing the capacity of the battery cell.